What condition is characterized by an abnormally reduced number of white blood cells in a sample of blood?

Leukocytopenia is the condition characterized by an abnormally reduced number of white blood cells, known as leukocytes, in the blood. White blood cells are crucial components of the immune system, helping to defend the body against infections and diseases. When the number of these cells is below the normal range, the body's ability to fight off infections can be significantly impaired.

Understanding the meaning of the term can help clarify why it is the correct choice. The prefix "leuko-" refers to white, and "-cytopenia" denotes a deficiency in cell numbers. Together, these components directly indicate a reduction in white blood cells.

The other conditions listed do not fit the description of having reduced white blood cells. Macrocytosis refers to red blood cells that are larger than normal, bacteremia indicates the presence of bacteria in the blood, and polycythemia is characterized by an increase in red blood cells. Each of these conditions addresses different aspects of hematologic health, underscoring the specificity of leukocytopenia in relation to white blood cell counts.